添加剂PVB对炭气凝胶制备工艺及结构的影响

采用溶胶—凝胶法,以间苯二酚(R)、甲醛(F)为原料、无水碳酸钠(C)作催化剂、聚乙烯醇缩丁醛(PVB)为添加剂、无水乙醇作溶剂,通过常温常压干燥和高温炭化制备炭气凝胶。考察了中间产物有机凝胶的热解行为和催化剂浓度及PVB用量对炭气凝胶孔隙结构的影响。结果表明:PVB的加入不仅加强了有机凝胶的网络结构,使其更利于常温常压干燥,而且能够较好地调控炭气凝胶的孔径分布;在一定的PVB加入量范围内,随着PVB加入量的增加,炭气凝胶的比表面积增加,孔径分布也更加集中;催化剂浓度对炭气凝胶的比表面积及孔径分布有较大的影响,当R/C=300,PVB/R=1/10时比表面积达到最大值(386m~2/g)。     

CuO(CoO,MnO)/SiO_2纳米复合气凝胶催化剂载体的制备及其在合成碳酸二苯酯中的应用

以正硅酸乙酯为硅源,以乙酸铜、乙酸钴和乙酸锰的水溶液为前驱体,采用溶胶–凝胶法和CO2超临界干燥工艺制备了CuO(CoO,MnO)/SiO2纳米复合气凝胶。采用场发射扫描电镜、透射电镜和电子散射能谱分析等对纳米复合气凝胶的微观结构和组成进行了表征。采用Brunauer–Emmett–Teller法测定了纳米复合气凝胶的比表面积、孔径及孔径分布。以纳米复合气凝胶为载体制备了负载型催化剂,用于催化合成碳酸二苯酯(diphenyl carbonate,DPC),并用气相色谱仪对反应液进行了分析。结果表明:纳米复合气凝胶的粒径为20～100nm,孔径为2～8nm,平均孔径为3.16nm,比表面积为664.4m2/g;过渡金属的摩尔含量为13.77%;催化合成DPC的质量收率达27.14%。     

厘米级SiO2气凝胶球体的制备及表征

以正硅酸乙酯(TEOS)为硅源,采用酸碱两步催化溶胶-凝胶法和CO2超临界干燥技术成功制备出完整的厘米级SiO2气凝胶球体.当配比条件为TEOS∶ EtOH∶ H2O=1∶10∶4时制备的SiO2气凝胶球体具有典型的纳米多孔网络结构.采用扫描电镜(SEM)、透射电镜(TEM)、傅里叶变换红外光谱仪(FT-IR)、孔径分布及比表面积测试仪(BET)、纳压痕技术对SiO2气凝胶球体的表面形貌、内部结构、化学成分、比表面积、孔径分布及力学性能进行研究分析.研究表明:低温有利于制备出完整的厘米级SiO2气凝胶球体.随着凝胶温度的增加,SiO2气凝胶球体样品的收缩率逐渐增加,而孔隙率和比表面积逐渐减小.当凝胶温度为-5℃时,厘米级SiO2气凝胶球体样品的平均孔径为24.8 nm,孔体积为4.9 m3/g,比表面积高达1004.38 m2/g,密度为0.104g/cm3,收缩率约为16.2％,孔隙率约为95.3％,弹性模量和硬度最大分别为8.79 MPa与5.24 MPa.     

二氧化硅气凝胶的制备和表征

以正硅酸四乙酯为硅源，通过采取老化、表面修饰、溶剂置换和分级干燥等一系列抑制二氧化硅气凝胶干燥中出现缩裂的有效措施，以非超临界干燥技术最终获得了大块无裂纹的二氧化硅气凝胶。该气凝胶的孔径较小且分布均匀，比表面积为684m^2／g，孔体积可达1．38cm^3／g，最可几孔径为3．221nm，平均孔径达2．871m。同时在实验和理论分析的基础上总结二氧化硅气凝胶缩裂的主要原因和抑制缩裂的有效措施。     

疏水SiO2气凝胶的制备及表征

以正硅酸乙酯(TEOS)为硅源,三甲基氯硅烷(TMCS)为改性剂,经老化、表面疏水改性,常压干燥制备了高比表面积疏水SiO2气凝胶.用傅立叶变换红外光谱仪(FT-IR)、扫描电镜(SEM)、比表面及孔径分布仪、热重分析仪(TG-DSC)对其疏水特性及结构进行表征.结果表明:疏水SiO2气凝胶与水的接触角达145°,在空气中的热稳定温度为269 ℃;且比表面积达1035 m2/g,具有典型的气凝胶结构特征,孔径尺寸和密度分别达9.7 nm和0.129 g/cc,骨架颗粒尺寸小于30 nm.     

水玻璃基低密度疏水二氧化硅气凝胶制备及性能研究

以水玻璃为硅源,通过酸碱两步溶胶-凝胶法及一步置换改性,常温常压下制备了低密度疏水性二氧化硅气凝胶。探讨了pH、老化方式及三甲基氯硅烷(TMCS)用量对凝胶时间、二氧化硅气凝胶表观密度和孔隙率的影响。采用冷场发射扫描电镜(FESEM)、比表面积及孔径分析仪(BET)、傅里叶变换红外光谱仪(FT-IR)和接触角测试仪分别研究了二氧化硅气凝胶的微观形貌、比表面积及孔径分布、改性效果及疏水性能。结果表明,二氧化硅气凝胶具有三维纳米网络结构,表观密度为0.130 1 g/cm3、孔隙率高达94.27%、比表面积为599 m2/g、平均孔径为10~30 nm、接触角为142°。     

雾化法常压干燥制备SiO_2气凝胶微球及其性能研究

以水玻璃为硅源,经离子交换制备硅溶胶,以甲酰胺为分散剂和干燥控制剂,混合后雾化喷入预制的油相中,结合其凝胶时间控制搅拌过程使之凝胶化成微球,并经过多次溶剂交换在常压干燥条件下获得粒径均匀、分散性好的SiO_2气凝胶微球。BET分析表明其比表面积约为709.3m~2/g,平均孔径为11.2nm;SEM分析表明微球直径约10~20μm,表面为连续网络纳米孔结构;FT-IR分析显示其在制备过程枝接了-CH_3,具有良好疏水性;DSC-TGA分析显示1000℃内具有良好的热稳定性。     

常压干燥法制备SiO2气凝胶粉体

以工业硅溶胶为原料,通过凝胶过程与干燥条件的控制,采用常压干燥法制备了SiO2 气凝胶粉体,并考察了老化液中正硅酸乙脂(TEOS)含量和干燥控制化学添加荆甲酰胺的添加对气凝胶粉体堆积密度、比表面积和孔径分布的影响.结果表明:所得气凝胶粉体具有纳米多孔结构,组成气凝胶结构的基本粒子呈圆球形,粒径为10～25 nm,由基本粒子连接而成的网络结构具有5～50 nm的孔径分布;随着热处理温度从常温升至1 100℃,SiO2气凝胶从最初的无定形态转化为方石英;在,TEOS的醇溶液中老化,有利于增强凝胶骨架的强度;添加甲酰胺可以改善气凝胶粉体的孔径分布,提高其比表面积.     

溶胶-凝胶工艺合成微孔-介孔钛硅复合材料

用硫酸催化醇盐水解,经溶胶-凝胶过程制备了微孔-介孔钛硅复合材料。通过X射线衍射(XRD)和低温N_2吸附-脱附测定,考察了水解pH值、温度、时间以及Ti/Si摩尔比等因素对产物孔道结构的影响。实验结果表明,在pH值2.5～3.0,温度60℃,反应时间2h的条件下进行钛、硅醇盐的水解聚合是较为有利的,合成产物具有短程有序的孔道结构,较窄的孔径分布,随Ti含量增加比表面积减小。以十六烷基三甲基溴化铵(CTAB)作模板剂得到的纯硅样品为平均孔径1.78 nm的微孔材料,具有866 m~2/g的比表面积;而含Ti产物为微孔-介孔材料,平均孔径略小于2 nm。以三嵌段聚合物(P123)作模板剂得到的含20%质量分率Ti的产物为介孔材料,平均孔径略小于4 nm,比表面积为618 m~2/g。     

溶剂顺序及配比对常压制备SiO_2气凝胶的影响

以硅溶胶为硅源,在氨水催化下硅溶胶变为凝胶,凝胶经溶剂替换和改性后在常压干燥条件下制备了SiO_2气凝胶。研究了不同溶剂顺序及配比对SiO_2气凝胶的影响。用扫描电镜对SiO_2气凝胶的形貌进行了表征,用比表面积及孔径分析仪对气凝胶的基本性质进行了分析,用综合热分析仪对气凝胶进行了热稳定性分析,结果表明,当乙醇、正己烷、三甲基氯硅烷的体积比为10:10:1时,气凝胶的气孔分布较为均匀,三维网络结构以及性能较好。     

纳米级增强体复合硅气凝胶的研究进展

二氧化硅气凝胶的脆性大、力学强度过低,严重限制了其应用领域。常规微米级或大于微米尺寸的增强体复合硅气凝胶可以提升硅气凝胶性能,但难以在纳米尺寸范围内对凝胶孔隙增强。目前,可以采用合成聚合物纳米纤维、纤维素纳米纤维、纳米管、无机纳米纤维、石墨烯及氧化石墨烯等增强硅气凝胶,纳米级增强材料能够均匀分散在硅气凝胶纳米孔隙中,干燥收缩小、孔比表面积大、可有效提升硅气凝胶抗压强度、改进韧性。     

Modelling of water adsorption by activated carbons: effects of microporous structure and oxygen content

The present paper examines the adsorption of water by microporous carbons containing various amounts of surface oxygen and a smaller proportion of basic centres. The modelling of water adsorption for 293 and 310 K, using variable pore size distributions (PSD), confirms that the overall type IV isotherm is the sum of a type I isotherm associated with the specific interactions, and a type V isotherm reflecting the non-specific interactions. The principle of temperature invariance is followed by these isotherms, which indicates that modelling leads to the Dubinin-Astakhov equation.The present approach allows the prediction of water adsorption near room temperature, on the basis of the PSD and the density of oxygen present on the surface area of the micropores. It is assumed, to a first and good approximation, that the pores are slit-shaped and the oxygen distribution is random.     

Influence of Catalyst (Citric Acid) Concentration on the Physical Properties of TEOS Silica Aerogels

In the present paper, the experimental results on the influence of catalyst (citric acid) concentration on the physical properties of TEOS silica aerogels, are reported. The aerogels have been prepared by hydrolysis and polycondensation of tetraethoxysilane (TEOS) using citric acid (CTA) as a new catalyst followed by supercritical drying in an autoclave. In order to obtain the best quality silica aerogels in terms of monolithy, high transparency, low density, large surface area and high porosity with uniform pore size distribution, the catalyst concentrations were varied from 0.0005 M to 0.1 M by keeping the molar ratio of TEOS : EtOH : H₂O constant at 1 : 5 : 7, respectively. It has been found that the lower (<0.001) CTA concentration resulted in low density, smaller surface area but opaque aerogels whereas higher (>0.005 M) CTA concentration resulted in high density, large surface area, highly transparent but cracked aerogels. On the other hand, medium (between 0.001 and 0.005 M) CTA concentration resulted in monolithic, low density, large surface area and highly transparent silica aerogels. The pore size distribution (PSD) for higher (0.1 M) and lower (0.0005) CTA concentrations shifted towards smaller and larger pore radii respectively, whereas for medium (0.001 M) CTA concentration, the PSD is narrow and uniform, which reduces the differential pressure during supercritical solvent extraction leading to monolithic silica aerogels. These results have been supported and discussed by considering the particle and pore sizes observed by Scanning Electron Microscopy (SEM). The surface area was measured by BET analysis.     

酸碱催化剂浓度对柔性硅气凝胶性能和结构的影响

以甲基三甲氧基硅烷(MTMS)和正硅酸乙酯(TEOS)作为混合硅源,甲醇为溶剂,十六烷基三甲基溴化铵(CTAB)为表面活性剂,通过酸碱两步催化溶胶凝胶法制备醇凝胶,经超临界干燥可以制备高弹性疏水块状硅气凝胶。分别采用0.1 mol·L^-1 和0.01 mol·L^-1 的草酸作为酸催化剂,5 mol·L^-1 和10 mol·L^-1 的氨水作为碱催化剂,研究不同酸碱催化剂浓度对其网络结构的影响。发现高浓度酸和高浓度碱以及低浓度酸和低浓度碱作为催化剂合成的硅气凝胶的网络结构更加均匀,孔径分布更窄。其中,在草酸浓度为0.01 mol·L^-1、氨水浓度为5mol·L^-1 时,所得硅气凝胶密度为0.135 g·cm^-3、比表面积为807 m²·g^-1、孔隙率约为93%,凝胶最大可压缩至其起始长度的60%,压缩回弹率为100%。     

毛竹纳米纤丝化纤维素/TiO2气凝胶的制备及表征

以钛酸四丁酯为原料,纳米纤丝化纤维素(NFC)为模板,制备NFC/TiO₂气凝胶。采用扫描电子显微镜(SEM)、X射线衍射(XRD)、傅里叶变换红外光谱(FT-IR)、比表面积及孔径分析仪对其进行表征。结果表明:NFC/TiO₂气凝胶中NFC保留了其原有的空间网络结构;TiO₂主要以颗粒的形式附着在NFC表面;通过BET分析可知其比表面积为12.55 m²/g,平均孔径为17.07 nm。     

Size control and characterization of spherical carbon aerogel particles from resorcinol-formaldehyde resin

Spherical resorcinol-formaldehyde (RF) aerogel particles were synthesized by emulsion polymerization of resorcinol with formaldehyde in a slightly basic aqueous solution, followed by supercritical drying with carbon dioxide. RF carbon aerogel particles were prepared by carbonizing of the RF aerogel particles at a high temperature under a nitrogen atmosphere. By changing the viscosity of the RF sol added to the cyclohexane containing a surface-active agent for preparation of the spherical RF hydrogels, we investigated the influence of the apparent viscosity of the RF sol on the size of the generated RF carbon aerogel particles. We could successfully prepare the RF carbon aerogel particles with a truly spherical shape and control their size in the range from about 10 to 500 μm by changing the apparent viscosity of the RF sol. The spherical RF carbon aerogel particles with an average diameter of 20 μm have a BET surface area of about 800 m²/g and a uniform mesopore radius of 1.78 nm.     

直接甲醇燃料电池用碳气凝胶载铂催化剂的研究

利用溶胶—疑胶方法制备了高比表面积的碳气凝胶,利用浸渍还原法制备了Pt/碳气凝胶和Pt/C催化剂。采用BJH和TEM考察碳气凝胶的孔径分布和金属粒子的大小与分布,循环伏安曲线测试考察Pt/碳气凝胶对甲醇催化氧化性能的影响。结果表明,碳气凝胶的比表面积达到480 m2/g,孔径分布良好,催化剂金属颗粒较小,分散较好,循环伏安曲线图显示出Pt/碳气凝胶比传统的Pt/C对甲醇催化氧化性能高。     

Effect of Attapulgite Pore Size Distribution on Soybean Oil Bleaching

The pore size distribution and specific surface area of the attapulgite was a crucial parameter for the uptake of pigments of oil. Bleaching of the soybean oil with three attapulgites with different pore size distribution, which were assigned a, b, and c, respectively was investigated. The specific surface area and the pore size distribution of the attapulgites were characterized. The Freundlich isotherm analysis was used to evaluate the sorption capacity of the three attapulgite. Sample b gave the highest surface area and sample c the lowest. Sample b exhibited a wider pore distribution (8–65 Å) whereas samples a and c had more micropores smaller than 15 Å. Sample a, in contrast to samples b and c, was characterized by some larger pores (100–170 Å). The sorption capacity followed the sequence: attapulgite sample c > attapulgite sample a > attapulgite sample b. The sorption capacity was decided by the pore size distribution. The more pores with a distribution range 8–32 Å (i.e., close to the diameter of the pigments), the more pigments removed. The attapulgite sample c, which had most pores (8–32 Å) was the best.     

Effects of silica aerogel particle sizes on the thermal–mechanical properties of silica aerogel – unsaturated polyester composites

Silica aerogels with a surface area as high as 773?m²?g^?1 and a density of 0.077?g?cm^?3 were produced from rice husk via sol–gel process and ambient pressure drying. A particulate composite material was prepared by adding silica aerogel particles of three different particle sizes (powder, granules and bead) to unsaturated polyester resin with a fixed volume fraction of 30%. Thermogravimetric and thermal conductivity studies revealed that silica aerogel composites were having higher thermal stability and thermal insulation than the neat resin. It was suggested that the preservation of aerogel pores from resin intrusion is important for better thermal properties. Larger silica aerogel particles have more porous area (unwetted region) which results in a lower degradation rate and lower thermal conductivity of the base polymer. However, the addition of silica aerogel into resin has reduced the tensile modulus of the polymer matrix where smaller particle size displayed higher toughness than those with bigger particle size.